Added note about creating 'root' group for cvsup/Linux.

doc/setup.txt

@@ -157,10 +157,14 @@ the testbed tree)
 
 Logs - To avoid filling up /var, link /var/log/testbed to /usr/testbed/log
 
-CVSUPD - Minor changes to images can be distributed at boot time with cvsup. See
-doc/newimage.txt for an overview of setting up a sup tree. Make sure to copy over
-the old one (if it exists), and make sure cvsupd is running (there's an example
-rc.d script in the rc.d/ directory of the testbed CVS tree)
+CVSUPD - Minor changes to images can be distributed at boot time with cvsup.
+See doc/newimage.txt for an overview of setting up a sup tree. Make sure to
+copy over the old one (if it exists), and make sure cvsupd is running (there's
+an example rc.d script in the rc.d/ directory of the testbed CVS tree.) Create
+a group named 'root', with any gid. This is because cvsup uses the game of
+the group, rather than its gid, to determine what group the file should belong
+to. Since Linux uses 'root' instead of BSD's 'wheel', this is needed for the
+Linux sup tree.
 
 Apache - You should have installed apache with mod_ssl, and php3 (NOTE: Version
 3.0.17 is known to have broken file uploading support. Use 3.0.16 or 3.0.18 -